void encodeJpegIntoOutputStream(
JNIEnv* env,
DecodedImage& decoded_image,
jobject os,
int quality) {
// jpeg does not support alpha channel
THROW_AND_RETURN_IF(
decoded_image.getPixelFormat() != PixelFormat::RGB,
"Wrong pixel format for jpeg encoding");
struct jpeg_compress_struct cinfo;
// set up error handling
JpegErrorHandler error_handler{env};
error_handler.setCompressStruct(cinfo);
if (setjmp(error_handler.setjmpBuffer)) {
return;
}
// set up OutputStream as jpeg codec destination
jpeg_create_compress(&cinfo);
JpegOutputStreamWrapper os_wrapper{env, os};
cinfo.dest = &(os_wrapper.public_fields);
// set up image properties
cinfo.image_width = decoded_image.getWidth();
cinfo.image_height = decoded_image.getHeight();
cinfo.input_components = 3;
cinfo.in_color_space = JCS_RGB;
jpeg_set_defaults(&cinfo);
jpeg_set_quality(&cinfo, quality, TRUE);
jpeg_start_compress(&cinfo, TRUE);
writeMetadata(cinfo, decoded_image);
// write all pixels, row by row
JSAMPROW row_pointer = decoded_image.getPixelsPtr();
const int stride = decoded_image.getStride();
while (cinfo.next_scanline < cinfo.image_height) {
if (jpeg_write_scanlines(&cinfo, &row_pointer, 1) != 1) {
jpegSafeThrow(
(j_common_ptr) &cinfo,
"Could not write scanline");
}
std::advance(row_pointer, stride);
}
jpeg_finish_compress(&cinfo);
jpeg_destroy_compress(&cinfo);
}
/**
* initialize input stream
*/
static void isInitSource(j_decompress_ptr dinfo) {
JpegInputStreamWrapper* src = (JpegInputStreamWrapper*) dinfo->src;
JNIEnv* env = src->env;
src->start = true;
src->javaBuffer = env->NewByteArray(kStreamBufferSize);
jpegJumpOnException((j_common_ptr) dinfo);
src->buffer = (JOCTET*) (*dinfo->mem->alloc_small)(
(j_common_ptr) dinfo,
JPOOL_PERMANENT,
kStreamBufferSize * sizeof(JOCTET));
if (src->buffer == nullptr) {
jpegSafeThrow(
(j_common_ptr) dinfo,
"Failed to allocate memory for read buffer");
}
}
/**
* Initialize output stream
*/
static void osInitDestination(j_compress_ptr cinfo) {
JpegOutputStreamWrapper* dest = (JpegOutputStreamWrapper*) cinfo->dest;
JNIEnv* env = dest->env;
// allocate java byte array
dest->javaBuffer = env->NewByteArray(kStreamBufferSize);
jpegJumpOnException((j_common_ptr) cinfo);
// allocate the output buffer --- it will be released when done with image
dest->buffer = (JOCTET *) (*cinfo->mem->alloc_small)(
(j_common_ptr) cinfo,
JPOOL_IMAGE,
kStreamBufferSize * sizeof(JOCTET));
if (dest->buffer == NULL) {
jpegSafeThrow(
(j_common_ptr) cinfo,
"Failed to allcoate memory for byte buffer.");
}
dest->public_fields.next_output_byte = dest->buffer;
dest->public_fields.free_in_buffer = kStreamBufferSize;
}
